Analysis of Aircraft Accuracy Location in Aeronautical Multilateration Systems Tiago Manuel Ribeiro Costa Thesis to obtain the Master of Science Degree in Electrical and Computer Engineering Supervisor: Prof. Luís Manuel de Jesus Sousa Correia Examination Committee Chairperson: Prof. José Eduardo Charters Ribeiro da Cunha Sanguino Supervisor: Prof. Luís Manuel de Jesus Sousa Correia Members of Committee: Prof. António Manuel Restani Graça Alves Moreira Eng. André Gustavo Botelho Maia June 2017 ii To my beloved family “I do not think that the wireless waves I have discovered will have any practical application.” Heinrich Rudolf Hertz “Truth is much too complicated to allow anything but approximations.” John von Neumann iii iv Acknowledgements I would like to express my sincere gratitude to my thesis supervisor, Prof. Luís M. Correia, for all the knowledge, guidance, motivation, consideration, and time, shared with me during the development of this thesis. Our weekly meetings were decisive for the success of this work. I would also very much like to thank NAV Portugal; particularly, Eng. Carlos Alves, Eng. André Maia, and Eng. Luís Pissarro, whose valuable input and feedback were paramount to the development, improvement, and technical relevance of this thesis. A special word goes also to all the friends at the Group for Research On Wireless (GROW), who directly or indirectly made this thesis possible, and without whom this work would have become a cumbersome task. I am also grateful to the friends, colleagues, faculty, and staff of the Department of Electrical and Computer Engineering at Instituto Superior Técnico, who have been with me during these last years, and much have contributed to what I am today. Finally, and most importantly, I would like to thank my family for their unwavering love, and support. Thank you all! v vi Abstract Aeronautical multilateration systems enable the locating of an aircraft based on the Time Difference of Arrival of its signal to three or more strategically placed receiving ground stations, located around an area of interest, providing continuous air traffic surveillance. The aim of this dissertation was to develop a model for the performance analysis of multilateration systems, concerning radio coverage and aircraft location accuracy. The proposed model considers ground stations’ location, their antennas radiation patterns, transmitted power, receiver sensitivity, and the corresponding parameters for the aircraft. Line of Sight conditions are assessed by considering Digital Elevation, Fresnel’s Ellipsoid, and the Effective Earth’s Radius Models. The Free-Space Path Loss Model is also used, with fading margins being set to model power oscillations due to multipath and the aircraft orientation uncertainty. Aircraft accuracy location is estimated from the system’s Geometric Dilution of Precision, considering error components due to tropospheric delay, multipath, receiver noise, quantisation, and clock bias. The model was implemented in a simulator and successfully validated, with results in agreement with data from the literature and previously implemented systems. The developed model was employed in the analysis of an implemented system from NAV Portugal, with results suggesting that the system has a good degree of redundancy, displaying negligible reductions in coverage, of as low as 2%, when two out of twelve ground stations are removed. A statistical analysis suggests that a Shifted Exponential Distribution can model the positioning error, with parameters proportional to the aircraft’s altitude. Keywords Air Traffic Control; Distributed Positioning Systems; Aeronautical Multilateration; Positioning Error. vii Resumo Os sistemas de multilateração aeronáutica permitem localizar uma aeronave com base na diferença do tempo de chegada de sinais a três ou mais estações terrestres, localizadas ao redor de uma área de interesse. O objetivo desta dissertação foi desenvolver um modelo para a análise do desempenho de sistemas de multilateração relativamente à precisão da localização de aeronaves. O modelo proposto considera a localização das estações terrestres e da aeronave, os diagramas de radiação das antenas, a potência transmitida, e a sensibilidade do recetor. As condições de Linha-de-Vista são avaliadas, considerando os Modelos de Elevação Digital, do Elipsoide de Fresnel, e do Raio Efetivo da Terra. O Modelo de Propagação em Espaço Livre é também empregue, considerando margens de desvanecimento para as oscilações de potência devido a multipercurso e à incerteza da orientação da aeronave. A precisão da localização da aeronave é estimada a partir da Diluição Geométrica de Precisão, considerando as componentes de erro devido ao atraso troposférico, multipercurso, ruído do recetor, quantização, e enviesamento do relógio. O modelo foi implementado num simulador e validado com sucesso, com resultados em concordância com dados da literatura e de sistemas previamente implementados. Um sistema da NAV Portugal foi analisado, com resultados que sugerem que o sistema possui uma boa redundância, apresentando até 2% de redução da cobertura, quando duas de doze estações terrestres são removidas. A análise estatística sugere que o erro de posicionamento pode ser modelado por uma Distribuição Exponencial Deslocada, com parâmetros proporcionais à altitude da aeronave. Palavras-chave Controlo de Tráfego Aéreo; Sistemas de Posicionamento Distribuídos; Multilateração Aeronáutica; Erro de Posicionamento. viii Table of Contents Acknowledgements ........................................................................................................................... v Abstract ........................................................................................................................................... vii Resumo .......................................................................................................................................... viii Table of Contents ............................................................................................................................. ix List of Figures ................................................................................................................................... xi List of Tables .................................................................................................................................. xiii List of Acronyms ............................................................................................................................. xiv List of Symbols .............................................................................................................................. xvii List of Software .............................................................................................................................. xxii 1 Introduction 1 1.1 Aeronautical surveillance paradigm ........................................................................................2 1.2 Aeronautical multilateration overview .....................................................................................3 1.3 Motivation, novelty, and content .............................................................................................4 2 Fundamental concepts and state of the art 7 2.1 Aeronautical surveillance systems ..........................................................................................8 2.2 Basic aspects of multilateration systems ............................................................................. 10 2.3 Performance parameters for multilateration systems .......................................................... 13 2.4 Technical limitations of multilateration systems ................................................................... 15 2.5 State of the art ...................................................................................................................... 17 3 Models and simulator description 21 3.1 Model development .............................................................................................................. 22 3.1.1 Model overview ....................................................................................................... 22 3.1.2 Propagation model .................................................................................................. 24 3.1.3 Error model ............................................................................................................. 30 3.2 Model implementation .......................................................................................................... 33 3.2.1 Simulator overview ................................................................................................. 34 3.2.2 Propagation model simulator .................................................................................. 35 3.2.3 Error model simulator ............................................................................................. 38 3.2.4 Estimating the required carrier-to-noise ratio ......................................................... 38 3.2.5 Radiation pattern of the ground stations’ antenna .................................................. 40 3.2.6 Statistical modelling of an antenna mounted on an aircraft.................................... 41 3.3 Statistical modelling of positioning error .............................................................................. 44 3.3.1 Descriptive statistics ..............................................................................................